System of manufacturing injection molded article and metal mold

ABSTRACT

In an injection process, molten resin is successively injected from a first flow channel and a second flow channel connected with each other in order into a cavity of a metal mold. High-temperature resin existing in the first flow channel is injected in advance into the cavity as a part of a single shot of molten resin to later form a skin layer of a molded article. other low temperature resin near a flowable limit existing in the second flow channel is subsequently injected into the cavity as another part of the single shot of molten resin to later form a core layer of the molded article. A low temperature resin remaining in the first flow channel when injection is completed is warmed to be a high-temperature resin before the next cycle, thereby allowing successive molding of molded articles.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is based on and claims priority to JapanesePatent Application 2018-169487, filed on Sep. 11, 2018 in the JapanPatent Office, the entire disclosure of which is hereby incorporated byreference herein.

BACKGROUND Technical Field

Embodiments of this disclosure relate to a system of manufacturing aninjection molded article and a metal mold.

Related Art

In a known manufacturing system of manufacturing an injection-moldedarticle, multiple shots of molten resin are supplied from multiplesources and are sequentially injected into a cavity.

In recent years, in a process of manufacturing injection moldedarticles, it is demanded that a molding cycle is further shortened. Inthis point of view, a known equipment disclosed in the first patentliterature has room for improvement, because it cannot sufficientlyshorten the molding cycle.

Various embodiments of the present disclosure have been made in view ofthe above-discussed problem, and a purpose thereof is to provide a novelsystem of manufacturing injection-molded articles and a metal moldcapable of effectively shortening a molding cycle.

SUMMARY

Accordingly, one aspect of the present disclosure provides a novelsystem of manufacturing injection molded articles. That is, in a moldinjection process of injecting molten resin into a cavity of a metalmold, high temperature molten resin having a given temperature isinjected in advance as a part of a single shot of molten resin into acavity to later form a skin layer of an injection-molded article. Othermolten resin having a low temperature near a flowable limit issubsequently injected into the cavity as another part of the single shotof molten resin to later form a core layer of the injection-moldedarticle.

Another aspect of the present disclosure provides a novel metal moldthat includes a flow channel to guide low temperature resin (hereinbelow referred to as a low temperature flow channel section) and a flowchannel to warm the low temperature resin (herein below referred to as ahigh temperature flow channel section). The high temperature flowchannel section includes a first flow channel located right before acavity of a metal mold to warm molten resin injected in an early stageas a part of a single shot of molten resin until a high temperature tolater form a skin layer of an injection molded article. The lowtemperature flow channel section includes a second flow channelconnected to the first flow channel to retain heat of molten resininjected after the early stage as another part of the single shot ofmolten resin at a low temperature near the flowable limit to later forma core layer of the injection molded article.

According to the above-described manufacturing system and the metalmold, by setting temperature of the molten resin that later forms thecore layer of the injection molded article to a low level near theflowable limit, a time for solidifying the molten resin after it isinjected into the cavity can be reduced. Hence, a molding cycle can beshortened. Further, by setting temperature of the molten resin thatlater forms the skin layer of the injection-molded article to a higherlevel and thereby lowering melt viscosity thereof, generation of aninjection molded article having a defective appearance can besuppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present disclosure and many of theattendant advantages of the present disclosure will be more readilyobtained as substantially the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings, wherein:

FIG. 1 is a diagram illustrating an exemplary general view of aninjection molding machine with a metal mold structure according to afirst embodiment of the present disclosure;

FIG. 2 is a cross-sectional view illustrating the metal mold of thefirst embodiment of the present disclosure;

FIG. 3 is a cross-sectional view illustrating the metal mold of thefirst embodiment of the present disclosure when molten resin is suppliedto a flow channel:

FIG. 4 is a cross-sectional view illustrating the metal mold of thefirst embodiment of the present disclosure when a cavity is filled withthe molten resin:

FIG. 5 is a cross-sectional view illustrating the metal mold of thefirst embodiment of the present disclosure when the molten resin in thecavity is solidified;

FIG. 6 is a cross-sectional view illustrating the metal mold of thefirst embodiment of the present disclosure when the metal mold is open:

FIG. 7 is a diagram schematically illustrating exemplary behavior ofmolten resin in an initial stage of filling during an injection process:

FIG. 8 is a diagram schematically illustrating exemplar) behavior of themolten resin in a medium stage of filling during the injection process;

FIG. 9 is a diagram schematically illustrating exemplary behavior of themolten resin during the injection process when the molten resin iscompletely filled;

FIG. 10 is a diagram schematically illustrating an exemplary change intemperature of the resin in the cavity during the cooling process; and

FIG. 11 is a cross-sectional view illustrating a metal mold of a secondembodiment of the present disclosure.

DETAILED DESCRIPTION

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views thereof,and in particular to FIG. 1, an injection molding machine 10 is providedto manufacture a molded article by performing injection molding. Theinjection molding is a system to obtain a molded article (i.e., aninjection molded article) by injecting molten material into a metal mold40 and cooling and solidifying the molten material.

The injection molding machine 10 includes a mold fastening section 31and an injection section 32. The injection section 32 heats and meltsresin material and injects a melting result into the metal mold 40.(Hence) The injection section 32 includes a molten resin supply source.The injection section 32 controls injection speed when resin flows thruthe metal mold 40 and controls pressure when the metal mold 40 has beenfilled with the resin. The mold fastening section 31 opens and closesthe metal mold 40 and removes the molded article therefrom or the like.The metal mold 40 includes a fixed mold 41 and a movable mold 42 and isinstalled in the mold fastening section 31.

As illustrated in FIG. 2, a cavity 43 is formed between the fixed andmovable molds 41 and 42 as a space. Resin filled into the cavity 43becomes a molded article when it is solidified therein. The movable mold42 is disposed to be able to approach and separate from the fixed mold41. Thus, the metal mold 40 can be opened when the movable mold 42 isseparated from the fixed mold 41 and closed when the movable mold 42approaches the fixed mold 41. In FIG. 2, the metal mold 40 is in aclosed state.

The fixed mold 41 includes a mounting plate 44 located on a side of theinjection section 32, a plate 45 to form a cavity 43 between itself andthe movable mold 42, and a spacer block 46 sandwiched between themounting plate 44 and the plate 45. The fixed mold 41 also includes ahot runner unit 47 mounting over the mounting plate 44 to the plate 45.These devices other than the hot runner unit 47 can adopt other knownsuitable configurations.

The hot runner unit 47 constitutes a flow channel ranging from a nozzle33 of the injection section 32 to the cavity 43 to keep molten resinmelted therein. In this embodiment of the present disclosure, the hotrunner unit 47 includes a sprue 51, a heat retention manifold 52, and awarming manifold 53. The hot runner unit 47 also includes a gate 54.

The sprue 51 is attached to the mounting plate 44 and is connected tothe nozzle 33. The sprue 51 includes a sprue flow channel 55. A sprueheater 56 is provided in the sprue 51. The heat retention manifold 52 islocated between the mounting plate 44 and the plate 45 and is connectedto the sprue 51. The heat retention manifold 52 includes a heatretention flow channel 57. The heat retention manifold 52 includes aheat retention heater 58.

Molten resin injected from the injection section 32 has a lowtemperature TL. Herein below, molten resin having has a low temperatureTL is referred to as low temperature resin 92. The sprue heater 56 andthe heat retention heater 58 are set to the low temperature TL orsimilar temperature. Hence, the sprue 51 and the heat retention manifold52 keep the low temperature resin 92 injected from the injection section32 warm at the low temperature TL. The low temperature TL is near aflowable limit temperature and is lower than a temperature TN of moltenresin injected into the cavity when an ordinary injection moldingoperation is performed (herein below, referred to as a normaltemperature TN).

The warming manifold 53 is located between the mounting plate 44 and theplate 45 and is connected to the heat retention manifold 52. The warmingmanifold 53 includes a warming flow channel 59. The warming manifold 53is provided with a warming heater 61. The gate 54 is a valve gate andincludes a valve body 62 disposed on the plate 45, a valve pin 63, and adriving section 64 to drive the valve pin 63. The valve body 62 isconnected to the warming manifold 53 and includes a valve flow channel65. The valve pin 63 is enabled to open and close a connection holeconnecting the valve flow channel 65 with the cavity 43. The valve body62 is provided with a valve heater 66.

Each of the warming heater 61 and the valve heater 66 is set to a hightemperature TH higher than the low temperature TL. The warming heater 61and the valve heater 66 warm molten resin remaining in the warming flowchannel 59 and the valve flow channel 65 until the high temperature TH.The high temperature TH is usually higher than an ordinary moldingtemperature TN, and is lower than either a resin color changetemperature or a resin decomposition temperature. Herein below, moltenresin warmed until the high temperature TH is referred to ashigh-temperature resin 91. In FIG. 3 and following drawings, todistinguish the high-temperature resin 91 and the low temperature resin92 from each other, a hatching pattern therefor is differentiated.However, the high-temperature resin 91 and the low temperature resin 92are basically the same resin with each other.

The warming flow channel 59 and the valve flow channel 65 collectivelyconstitute a first flow channel 71 located just before the cavity 43.The warming manifold 53 and the gate 54 collectively constitute a hightemperature flow channel section 75. As illustrated in FIG. 3, the hightemperature flow channel section 75 is enabled to warm molten resininjected in an early stage as a part of a single shot of molten resin tolater form a skin layer (i.e. a surface layer section) of a moldedarticle until the high temperature TH. Here, a capacity ofhigh-temperature resin 91 is desirably equal to or more than a productobtained by calculating the below described formula:

Capacity of Single shot×6/Maximum Thickness×Thickness of Skin Layer.

Here, since it varies depending on a type of resin, temperature and atime for filing thereof, the thickness of the skin layer is setaccordingly.

The sprue flow channel 55 and the heat retention flow channel 57collectively constitute a second flow channel 72 connected to the firstflow channel 71. The sprue 51 and the heat retention manifold 52collectively constitute a low temperature flow channel section 76. Thelow temperature flow channel section 76 is partially enabled to retainheat of molten resin injected after the early stage as another part ofthe single shot of molten resin to later form a core layer (i.e. aninterior) of the molded article at the low temperature TL.

As illustrated in FIGS. 3 and 4, by pumping out a single shot of moltenresin from the nozzle 33 to the second flow channel 72 and the firstflow channel 71 in order, the injection section 32 (see FIG. 1) pushesout a high-temperature resin 91 in the first flow channel 71 to thecavity 43 in advance, and subsequently pushes out a low temperatureresin 92 in the second flow channel 72 to the cavity 43. As illustratedin FIG. 5, the resin is filled and solidified in the cavity 43 therebybecoming a molded article 20.

The high-temperature flow channel section 75 is enabled to warm the lowtemperature resin 92 until the high temperature TH within a given periodof time calculated by summing up a cooling period of time for coolingand solidifying the resin as illustrated in FIG. 5 after the cavity 43is filled with resin as illustrated in FIG. 4, a mold opening period oftime for opening the metal mold 40 and ejecting the molded article 20 asillustrated in FIG. 6, and a metal mold closing period of time forclosing the metal mold 40 as illustrated in FIG. 3. In this embodimentof the present disclosure, the low temperature resin 92 is warmed untilthe high temperature TH within the total of the cooling period of timeand the mold opening period of time, for example.

The warming manifold 53 is connected to the heat retention manifold 52through a connection section 81. Between the warming manifold 53 and theheat retention manifold 52, a void 82 is provided excluding a positionof the connection section 81. The void 82 suppresses heat transferbetween the warming manifold 53 and the heat retention manifold 52. Inother words, the void 82 acts as a heat-transfer suppression section.

Now, a system of manufacturing a molded article by using an injectionmolding machine 10 is described. The injection molding machine 10manufactures a molded article by repeating the following first to fourthprocesses. A cycle of molding molded articles with the manufacturingsystem starts when the first process starts and ends when the fourthprocess is completed.

First, a metal mold closing process is described. As illustrated in FIG.3, the metal mold 40 is closed in a metal mold closing process. It issupposed that when the mold closing process starts, the low temperatureresin 92 remaining in the second flow channel 72 and the hightemperature resin 91 remaining in the first flow channel 71 during thelast molding cycle exist as are.

Secondly, in an injection process, as illustrated in FIG. 4, moltenresin is successively injected from the first flow channel 71 and secondflow channel 72 connected with each other in order into the cavity 43.At this moment, high-temperature resin 91 existing in the first flowchannel 71 is injected into the cavity 43 in advance as a part of asingle shot of molten resin to later form a skin layer 21 of a moldedarticle 20 (see FIG. 6). Further, low temperature resin 92 existing inthe second flow channel 72 is subsequently injected into the cavity 43as another part of the single shot of molten resin to later form a corelayer 22 of the molded article 20 (see FIG. 6).

In the injection process, since a single shot of molten resin is fedfrom the nozzle 33 to the second flow channel 72 and the first flowchannel 71 in this order, the high-temperature resin 91 in the firstflow channel 71 is pushed out in advance to the cavity 43, and the lowtemperature resin 92 in the second flow channel 72 pushed out to thecavity 43 thereafter. In other words, in the injection process, the hightemperature resin 91 located in the heat retention flow channel 57 andthe sprue flow channel 55, and the low temperature resin 92 located inthe valve flow channel 65 and the warming flow channel 59 are almostpushed by the low temperature resin 92 emitted from the nozzle 33thereby being filled into the cavity 43 in this order.

It is known as a filling behavior of molten resin shown during theinjection process that the molten resin almost gushes out from near athickness center at a tip of a flow thereof. Such a filling behavior iscalled a fountain flow. The filling behavior is now described withreference to a schematic diagram. First, as illustrated in FIG. 7, ahigh-temperature resin 91 flows into the cavity 43 in advance. Then, asillustrated in FIG. 8, a low temperature resin 92 coming thereafterpasses through a center portion of the cavity 43 while pushing theprecedent high temperature resin 91. The high-temperature resin 91 isthen pushed by the low temperature resin 92 and spreads toward an innersurface (i.e. a transfer surface) of the cavity 43. In the end, asillustrated in FIG. 9, the high temperature resin 91 filled in thecavity 43 forms a skin layer 21 and the low temperature resin 92 filledin the cavity 43 forms a core layer 22.

Now, an exemplary cooling process executed while warming resin shot nexttime until high-temperature is described herein below. As illustrated inFIG. 5, in the cooling process, the gate 54 is closed and the resinfilled in the cavity 43 is cooled while resin pushed out next time inadvance is warmed until a high temperature TH. Here, the resin pushedout next time in advance means low temperature resin 92 located in thevalve flow channel 65 and the warming flow channel 59 when the injectionprocess is terminated.

Now, a change in temperature of resin stored in the cavity 43 during acooling process is described in comparison to a comparative example. Inthe comparative exam, all of molten resin filled into the cavity has anormal temperature TN. As illustrated in FIG. 10, in the comparativeexample, a temperature TS−1 of the skin layer becomes a takeoutallowable temperature TR or less shortly after a time t0. The takeoutallowable temperature TR is near a melting temperature, at which amolded article is removable from a metal mold, for example. Further, atemperature Tc−1 of the deepest portion of the core layer becomes thetakeout allowable temperature TR or less at a time t2 when asolidification time T1 has elapsed after the time t0.

By contrast, according to the first embodiment of the presentdisclosure, a temperature Ts−2 of the skin layer becomes the takeoutallowable temperature TR or less soon after the time t0. Further, sincean initial value of a temperature Tc−2 of the deepest portion of thecore layer (of the first embodiment) is set lower than an initial valueof a temperature Tc−1 of the comparative example, the temperature Tc−2of the deepest portion of the core layer becomes the takeout allowabletemperature TR or less at a time t1 when a solidification time T2shorter than the solidification time T1 has elapsed. Hence, in the firstembodiment of the present disclosure, the cooling process can be moreshortened than that that in the comparative example by an amount of timedifference (T1−T2) between the solidification times T1 and T2. Theabove-described time difference (T1−T2) varies depending on a shape ofthe molded article and a type of resin as used or the like.

Now, an exemplary mold opening process executed while warming resinuntil high-temperature for the next shot is described. In the moldopening process, as illustrated in FIG. 6, the metal mold 40 is openedand a molded article 20 is ejected. In this process, resin to be pushedout next time in advance is successively warmed until a high temperatureTH.

As described heretofore, according to the first implementation of thepresent disclosure, during the injection process, molten resin issuccessively injected into the cavity 43 of the metal mold 40 from thefirst flow channel 71 and the second flow channel 72 connected with eachother in this order. High-temperature resin 91 existing in the firstflow channel 71 is injected in advance into the cavity 43 as a part of asingle shot of the molten resin to later form the skin layer 21 of themolded article 20. Further, low temperature resin 92 near the flowablelimit existing in the second flow channel 72 is subsequently injectedinto the cavity 43 as another part of the single shot of the moltenresin to later form a core layer 22 of the molded article 20.

According to the manufacturing system, since a temperature of moltenresin that later forms a core layer of the injection molded article iscontrolled to be a low level near the flowable limit, a time forsolidifying resin after it is injected into the cavity can be reduced.Hence, a molding cycle can be shortened. Further, a temperature ofmolten resin that later forms a skin layer of the injection-moldedarticle is controlled to be a higher level, generation of an injectionmolded article having a defective appearance can be suppressed.

Further, according to the first embodiment of the present disclosure, bysending single shot of the molten resin from the injection section 32 tothe second flow channel 72 and the first flow channel 71 in this orderin the injection process, the high temperature resin 91 in the firstflow channel 71 is pushed out into the cavity 43 in advance, andsubsequently the low temperature resin in the second flow channel 72 ispushed out into the cavity 43. Thus, since the high temperature resin 91and the low temperature resin 92 can be injected into the cavity 43 inorder by simply injecting the single shot without switching channels andsupply sources or the like, the molding cycle can be shortened.

Further, according to the first embodiment of the present disclosure,the manufacturing system includes: a mold closing process of closing ametal mold 40 as a previous process executed prior to an injectionprocess; a cooling process of cooling resin injected into the cavity 43as a post injection process; and a mold opening process of opening themetal mold 40 and ejecting a molded article 20 after the cooling processis ejected. In the cooling process and the mold opening process, moltenresin located in a flow channel just before the cavity 43, i.e., thefirst flow channel 71, is warmed until a high temperature TH. As aresult, without additionally imposing a process of warming the resin tobe injected into the cavity 43 next time in advance until the hottemperature TH, a high-temperature resin 91 can be prepared in parallelto the existing process.

Further, according to the first embodiment of the present disclosure, afixed mold 41 of the molding metal mold (40) includes thehigh-temperature flow channel section 75 and the low temperature flowchannel section 76. The high temperature flow channel section 75includes the first flow channel 71 located just before the cavity 43 ofthe metal mold 40 and is enabled to warm the molten resin injected in anearly stage as a part of a single shot of molten resin to later form askin layer 21 of the molded article 20 until the high temperature TH.The low temperature flow channel section 76 includes the second flowchannel 72 connected to the first flow channel 71 to reserve heat ofmolten resin injected after the early stage as another part of thesingle shot of molten resin to later form the core layer 22 of theinjection molded article 20 at the low temperature TL near the flowablelimit.

According to the injection molding machine 10, since a low temperatureTL near the flowable limit is set as a temperature of a molten resin tolater form a core layer 22 of a molded article 20, a solidification timefor solidifying resin injected into the cavity can be reduced. As aresult, a molding cycle can be shortened. Further, since molten resin toform a skin layer 21 of a molded article 20 is warmed until a relativelyhigh temperature, generation of a molded article 20 having a defectiveappearance can be suppressed.

Further, according to the first embodiment of the present disclosure,the injection molding machine 10 includes the injection section 32acting as a supply source of molten resin. By sending a single shot ofmolten resin to the second flow channel 72 and the first flow channel 71in order, the molten resin supply source pushes out the high-temperatureresin 91 in the first flow channel 71 in advance and the low temperatureresin 92 in the second flow channel 72 subsequently to the cavity 43.Thus, since the high temperature resin 91 and the low temperature resin92 can be injected into the cavity 43 in order by simply injecting thesingle shot without switching channels and supply sources or the like,the molding cycle can be shortened.

Further, according to the first embodiment of the present disclosure,the high-temperature flow channel section 75 is enabled to warm the lowtemperature resin 92 until the high temperature TH within a given periodof time calculated by summing up a cooling period of time for coolingthe resin filled in the cavity 43, a period of time for opening themetal mold 40 and ejecting the molded article 20, and a period of timefor closing the metal mold 40. Hence, even if a waiting time for warmingresin injected next time into the cavity 43 in advance until a hightemperature TH is not employed, high-temperature resin 91 can beprepared in parallel with an existing operation within an existingoperation period of time.

Further, according to the first embodiment of the present disclosure,since the low temperature flow channel section 76 includes the heatretention manifold 52 and the high temperature flow channel section 75includes the warming manifold 53, high-temperature resin 91 and lowtemperature resin 92 injected next time into the cavity 43 can beprepared in the hot runner unit 47. Further, since the hot runner unit47 can be preferably placed, for example, in accordance with a layoutbetween the injection section 32 and the molded article 20, degree ofdesign freedom increases.

Further, according to the first embodiment of the present disclosure,the void 82 is provided between the warming manifold 53 and the heatretention manifold 52 to suppress heat-transfer from the warmingmanifold 53 to the heat retention manifold 52. This can maintain adifference in temperature between the high-temperature resin 91 and thelow temperature resin 92.

Now, a second embodiment of the present disclosure is described. In asecond embodiment of the present disclosure, as illustrated in FIG. 11,the high temperature flow channel section 75 is a sprue 51, and thefirst flow channel 71 is a sprue flow channel 55. The low temperatureflow channel section 76 is the injection section 32, and the second flowchannel 72 is a flow channel formed in the nozzle 33 and the injectionsection 32 connected to the nozzle 33. Remaining configurations of thesecond embodiment of the present disclosure are similar toconfigurations of the first embodiment of the present disclosure, andare accordingly possible to obtain the similar advantages as obtained bythe first embodiment of the present disclosure. Further, according tothe second embodiment of the present disclosure, the metal mold 40 canbe smaller, thereby downsizing a molding system.

Another embodiment is herein below described. As a yet anotherembodiment of the present disclosure, resin to be pushed out next timein advance can be warmed until a high temperature during either one ofthe cooling process, the mold opening process, and the mold closingprocess or all of the processes. Further, in the other embodiment of thepresent invention, resin to be pushed out next time in advance can bewarmed until a high temperature in either one of the cooling period oftime, the mold opening period of time, and the mold closing period oftime or all of operation periods of time.

According to yet another embodiment of the present inventions, since thepresent invention is not limited to the void, the transmissionsuppression control section may be composed of a heat insulator or thelike.

The present invention is not limited to the above-described embodimentsand can be implemented in various manners not deviating from a point ofthe present invention.

Numerous additional modifications and variations of the presentdisclosure are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, thepresent disclosure may be executed otherwise than as specificallydescribed herein. For example, the system of manufacturing aninjection-molded article is not limited to the above-described variousembodiments and may be altered as appropriate. Similarly, the mold isnot limited to the above-described various embodiments and may bealtered as appropriate.

What is claimed is:
 1. A system of manufacturing an injection-moldedarticle comprising: a metal mold having a cavity to mold theinjection-molded article; and an injector to pump and inject moltenresin into the cavity, the injector injecting molten resin having a hightemperature into the cavity in advance as a part of a single shot ofmolten resin to later form a skin layer of the injection molded article,the injector subsequently injecting molten resin having a lowtemperature near a flowable limit into the cavity as another part of thesingle shot of molten resin to later form a core layer of the injectionmolded article.
 2. The system as claimed in claim 1, further comprising:a first flow channel to guide molten resin downstream; and a second flowchannel connected to the first flow channel to guide molten resindownstream, wherein the high-temperature molten resin is prepared bywarming molten resin in the first flow channel before the molten resinis pushed out into the cavity in advance, wherein the low temperaturemolten resin is prepared by retaining temperature of molten resin in thesecond flow channel before the molten resin is subsequently pushed outto the cavity, wherein the injector sends the single shot of moltenresin from a molten resin supply source to the second flow channel andthe first flow channel in order.
 3. The system as claimed in claim 2,wherein the first flow channel is located closer to the cavity than thesecond flow channel is, wherein the molten resin in the first flowchannel is warmed until the high temperature to prepare the hightemperature molten resin in at least one of: when the metal mold isclosed before molten resin is injected into the cavity, when moltenresin injected into the cavity is cooled, and when the metal mold isopened and an injection-molded article is removed from the metal moldafter the molten resin is cooled.
 4. The system as claimed in claim 1,further comprising: a nozzle section to send a single shot of moltenresin supplied from a molten resin supply source; and a cylinder,wherein the high temperature molten resin is prepared by warming themolten resin either in the nozzle section or in the vicinity thereof,wherein the relatively low temperature molten resin is prepared byretaining temperature of molten resin in the cylinder.
 5. A metal moldcomprising: a high temperature flow channel section to warm molten resininjected in an early stage as a part of a single shot of molten resinuntil a high-temperature, the molten resin later forming a skin layer ofan injection-molded article, the high temperature flow channel sectionhaving a first flow channel located just before a cavity of a metalmold; and a low temperature flow channel section to retain temperatureof other molten resin injected after the early stage of injection asanother part of the single shot of molten resin at a low level near aflowable limit, the other molten resin later forming a core layer of theinjection molded article, the low temperature flow channel sectionhaving a second flow channel connected to the first flow channel.
 6. Themetal mold as claimed in claim 5, further comprising a molten resinsupply source to push out the high temperature molten resin in the firstflow channel in advance and the low temperature molten resin in thesecond flow channel subsequently to the cavity by pumping a single shotof molten resin to the second flow channel and the first flow channel inthis order.
 7. The metal mold as claimed in claim 5, wherein thehigh-temperature flow channel section is enabled to warm the lowtemperature molten resin until the high temperature within a givenperiod of time calculated by summing up a cooling period of time forcooling a molten resin filled in the cavity, a period of time foropening the metal mold and ejecting an molded article, and a period oftime for closing the metal mold.
 8. The metal mold as claimed in claim5, wherein the low temperature flow channel includes a heat retentionmanifold and the high temperature flow channel includes a warmingmanifold.
 9. The metal mold as claimed in claim 8, further comprising aheat transfer suppression section to suppress heat transfer from thewarming manifold to the heat retention manifold, the heat transfersuppression section disposed between the warming manifold and the heatretention manifold.